US2794146A - Ultra-high frequency amplifying tube - Google Patents

Description

May 28, 1957 R. WARNECKE ETAL 2,794,146

ULTRA-HIGH FREQUENCY AMFLIFYING TUBE Filed Feb. 16. 1950 6 Sheets-Sheet l LJUII'MA- Q'Zby I May 28, 1957 R. WARNECKE ETAL 2,794,146

ULTRA-HIGH FREQUENCY AMPLIFYING TUBE Filed Feb. 16, 1950 6 Sheets-Sheet 2 Fig.4 4/

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May 28, 1957 R. WARNECKE ET AL 2,794,146

ULTRA-HIGH FREQUENCY AMFLIFYING TUBE Filed Feb. 16, 1950 6 Sheets-Sheet 3 an't-4J0- 5'.

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May 28, 1957 R. WARNECKE ETAL 2,794,146

ULTRA-HIGH FREQUENCY AMPLIFYING TUBE 6 Sheets-Sheet Filed Feb. 1 6. 1950 MUN/um Mlau, I H-am y 1957 R. WAR.NECKE ET AL 2,794,146

ULTRA-HIGH FREQUENCY AMPLIFYING TUBE Filed Feb. 16, 1950 6 Sheets-Sheet 5 May 28, 1957 R. WARNECKE ETAL 4 ULTRA-HIGH FREQUENCY AMPLIFYING TUBE Filed Feb. 16, 1950 6 Sheets-Sheet 6 n d, SW95 7 ULTRA-HIGH FREQUENCY AIVIPLIFYING TUBE Robert Warnecke, Werner Kleen, Harry Huber, and Oskar Dollies, Paris, France, assignors to Compagnie Generale de Telegraphic Sans Fil, a corporation of. France Our invention relates to a thermionic tube, the principle of which is based on the interaction between a plurality of electron beams which move at different speeds inside a discharge space, in which there exist a transverse electric field and a magnetic field directed at right angles with respect to the direction of the beam and to that of the electric field. Tubes are known in which an inter action between a plurality of electron beams moving at different speeds is used to obtain amplification. However, the tube according to our invention differs from such tubes by the fact'that it has the three following features simultaneously:

(a) A plurality of electron beams moving in thesame direction at different average speeds.

(b) An electric field which is constant in time and is directed in a direction at right angles to the direction of the mean propagation of the beams.

(c) A magnetic field which is constant in time and the direction of which is at right angles to the direction of mean propagation of the beam and to the direction of the electric field which is constant in time. I

It should be noted that a plurality of electron beams can also be replaced by a single beam of finite cross-section, the average speed of the electrons varying inside said cross-section. When hereinafter mention is made of a plurality of beams, it is therefore to. be understood that said beams can be replaced by a single beam with a variable speed of the electrons inside the cross-section of the beam. 7

In order to enable the principle of the invention to be understood, a description will first be given, with reference to Figs. 1 to 3, of the mechanism of the tube and then various embodiments thereof will be described with reference to Figs. 4 to 9. The explanations of the principle of the tube according to the invention will at the same time render apparent a number of appreciable advantages of the novel principle with respect to known tubes.

Figs. 1 to 3 are diagrammatic showings;

Fig. 4 is a longitudinal section of an example of tube according to the invention;

Fig. 4a is a sectional view of along the line EE' of Fig. 4;

Figs. 5 and 6 are longitudinal sections of other embodiments of the invention;

Fig. 7 is a longitudinal section of still another embodiment of the invention;

Fig. 7a is a sectional view of the tube of Fig. 7, taken along the line FF' of Fig. 7; T H

Figs. 8 and 8a are respectively longitudinal and crosssectional views of a further embodiment of the invention; a

Figs. 9 and 9a are respectively longitudinal and crosssectional views of still another embodiment of the invention. I

Fig. 1 is intended to explain the principle of themvention. In this figure, 1 and 2 represent the plates of the tube of Fig. 4, taken Patented May 28,

2 a capacitor, between which there exists an electrostatic field E which is directed along the axis x and is produced by an external source U. A magnetic field, at right angles to x, is applied in the direction +2 with a magnetic induction B. Into said capacitor penetrate two electron beams 3 and 4 which pass through the capacitor at different speeds v and v,. It will be assumed that the'movement of the electrons is straight as shown in Fig. 1, methods for obtaining such a movement of the electrons being described hereinafter, and its being pointed out on the other hand that the principle of the tube is not altered if the movement of the electrons is not straight. Before entering the capacitor, at least one of the beams is density modulated, i. e. one of the beams (or both of them) has, besides its direct current, an alternating current component. This alternating current component is produced by the signal to be amplified by means of a circuit, the various possible forms of which will be discussed hereinafter. At .the output end of the capacitor, the beams 3 and 4 transfer their alternating current to arioscillating circuits, this transfer being shown diagrammatically in Fig. l by a collector 6 to which the oscillating circuit is coupled. The mechanism of the tube is based on the fact that the alternating current contained in one of the beams or in both of them, increases from the input end to the output endand the control power of the beam is lower than the power transferred to the output cir-. cuit S, in other words there is a gain of power between the input and the output of the tube. J. I In order to be able to understand the mechanism of the increment of the alternating current along the beams, it is necessary to remember a few fundamental laws of the movement of the electrons in intersecting electric and magnetic fields. I If, in Fig. 1, there existsa longitudinal electric field in the direction *:y, the electron is subjected to a force directed towards ix. If, in Fig. 1, there exists a transverse electric field directed towards ix, an electron is subjected to a force in the direction 1y.

An electron beam will first be considered in which all the electrons are moving at the same speed (Fig. 2). The

beam is density modulated before it enters the intersect-, ing electric and magnetic fields. The density modulation means that the space charge varies periodically insidelthev beam. It will be assumed that in Fig. 2, the region A contains the highest density of the space charge, while in the region B the density thereof is lower. The lines of the A; C. electric fields produced by the negative charges of the electrons are then of the shape shown in continuous lines in Fig. 2. The forces exertedon the electrons according to the laws hereinbefore defined, are,

shown by arrows in broken lines. Leaving aside in the first place the transverse movement, it can be seen that,

owing to these forces, a grouping of electrons is produced in the region C, this grouping being out of phase with respect to the grouping due-to the original density modulation of the beam. Such a grouping obviously does not increase the alternatinghcurrent in the beam; in order to obtain this result, it is necessary to shift the phase of the grouping in C in such a manner that it falls in the region A. I if it is now assumed that the beam is out along DD crease in the alternating current along the path of the electrons, and consequently an amplification.

This explanation is only a rough one, but it is sufiicient to enable the phenomena to be understood qualitatively.

It should be pointed out that identical phenomena of increase of the grouping by interaction between two electron beams already occur in tubes inside which there exist neither a transverse electric field, nor a magnetic field at right angles to said electric field and to the direction of the beam. However, the tube according to the invention has a very substantial advantage with respect to the structures without intersecting electric and magnetic fields. In this latter case, the grouping in the lower speed beam is obtained at the expense of the speed of the other beam. From the power standpoint, it is only possible to convert into A. C. power the energy which corresponds to the difference of speeds between the two beams. Since this difference of speeds has to be small, otherwise the interaction between the beams would not take place, this corresponds to restricting the power and the efficiency of the tube. In the tube according to the invention, this restriction does not exist. The longitudinal speed of each beam, and therefore also the difference between the speeds, are retained throughout the travel of the beams. The grouped electrons which move in a retarding field do not lose speed but move, according to the laws hereinbefore defined, towards the positive plate of the capacitor. Electron trajectories such as those shown in Fig. 3 are obtained for each of the beams 3 and 4. However, the speeds of the electrons along the entire path are not altered. If, for example, an electron in the absence of the radio-frequency field at the input has a velocity the energy corresponding to 3 1 1 dz? 's 0 is converted into useful A. C. power. If all the electrons describe identical trajectories, an efiiciency of about 50% is obtained. Tests have in fact shown that efliciencies of this order of magnitude are obtained, which are of considerably higher values than those of the tubes in which two beams travel at different speeds but in which there are no intersecting electric and magnetic fields. As compared with such known tubes, the tube according to the invention has the advantage of having a substantially higher'efiiciency and useful power.

Tubes are furthermore known in which an electron beam interacts with an electromagnetic wave, this interaction also taking place in a space in which there exist intersecting electrostatic and magnetic fields. Such tubes have been described in our co-pending United States patent applications, Serial No. 794,164 filed on December 27, 1947, now Patent No. 2,511,407, and Serial No. 23,063 filed on April 24, 1948, now Patent No. 2,566,087. The efiiciency of these latter tubes is also fairly high. However, the tubes according to the invention have the following advantage: in the tubes according to the aforesaid patent applications, the interaction space is provided in the form of a retardation line that guides and retards the wave, since the speed of said wave has to be equal to that of the electrons in order that amplification shall take place. Said line is rather diificult to construct and the accuracy required for the dimensions is higher as the retardation of the guided wave is greater. While it is possible, for example, to construct retardation lines in which the speed of the wave is one twentieth of the speed of light, a reduction to one fiftieth for example already requires a mechanical accuracy which can only be obtained at very great expense. The voltage applied, and also the requisite magnetic field, have to be greater as the speed of the Wave is higher. This fact restricts in practice at the present time the construction of tubes according to the aforesaid patent applications to applied, voltages which are higher than 1 kilovolt and to magnetic fields which are greater than about 500 gauss.

On the other hand, in the new tube according to the present invention, the interaction space does not contain any line, or any tuned circuit element. As compared with the tubes of the aforesaid patent applications, it can be said that in the new tube, each elemental beam of the multiplicity of beams replaces the retardation line in its action on the other elemental beams.

Consequently, the mechanical difliculties are substantially smaller in the new tube than in the tubes according to the aforesaid patent applications. In particular, it is possible to construct, according to the principle of the present invention, tubes that operate with fairly low applied voltages, of a few hundred volts, and with magnetic inductions of about to 200 gauss. As regards the practical use of the tube, it is obvious that these facts represent important advantages.

Before giving constructional examples of tubes, its principle will be once more summarized.

The tube is a thermionic amplifying tube, the amplification being obtained by the'interaction of a multiplicity of electron beams which move at different speeds inside a space subjected to the action of intersecting magnetic and electric fields. At least one of the beams is density modulated. The interaction between the A. C. electric fields which are produced by the A. C. space charge of the modulated beam causes an increase in the grouping along the beams, i. e. an increase in the alternating current from the input end to the output end of the tube. Owing to this interaction, the beams move towards the positive electrode which produces the electrostatic field. At the output end of the tube the beams pass through an oscillating circuit and transfer their A. C. power to same.

According to these considerations of principle, it is necessary to produce beams which move at different speeds in intersecting electric and magnetic fields, it being possible to replace the multiplicity of beams by a single beam of finite cross-section, the speed being variable inside each cross-section of the beam. In the intersecting electric field E and magnetic field H, the average speed of the electrons in the direction at right angles to said fields is given by:

v :E B

wherein E is measured in v./cm., B in vs./sq. cm., B being the induction of the magnetic field. If B is measured in gauss, v in cm./s. is given by:

E 8 v 10 B According to the invention, in the cross-section of the interaction space, the ratio E/B is rendered variable, either by a variation of E, or by a variation of B, or by a variation of both in each cross-section of the interaction space. It is not necessary for the direction of variation of E/B to be predetermined, i. e. starting from the negative electrode of the capacitor the ratio E/B may either increase, or decrease towards the positive electrode of the capacitor.

The variation of B in the cross-section of the interaction space is generally obtained by means of a particular structure of the pole pieces of the magnet used, said pole pieces being of such a shape that a non-homogeneous magnetic field is produced.

The variation of the electric field inside each crosssection of the interaction space is obtained by means of the suitable shape of the electrodes that produce said a r-sm e field. If the electrodes are cylinders for example,the electric field at a point r is given by:

V being the potential difference between the two cylinders of radii r1 and r2.

Another method of obtaining an electric field which varies with the distance is based on the effect of the space charge on the shape of the potential between the two plates. Incandescent cathodes are introduced into this field and the current of said cathodes changes, by means of its space charge, the shape of the field; this method is applied by way of example in the embodiment of Fig. 9.

In the considerationsof principle, there were taken as a basis two beams that move in the absence of the radiofrequency field along straight lines. It is possible to obtain such beams by means of a plurality of cathodes which are at different potentials with respect to the negative plate of the capacitor, and the beams produced by said cathodes are introduced at different levels into the 'interaction space. However, tests have shown that the operation of the tube is not restricted to the existence of straight beams. It is also possible to produce the beam by means of a single equipotential cathode and introduce the beam. of finite cross-section into the interaction space. In the various points of the space, the average speed of the electrons is always that which is given by the ratio E/B; it therefore varies if E/B varies. A rotary movement is thus superposed on the average movement of the electrons, the trajectories of the electrons being formed by straight lines on which epicycloids are superposed. The elemental beams are then mixed with one another, but if E/B is variable in the cross-section, there are adjacent each electron other electrons which are moving at different average. speeds. The tubes are therefor provided, either with different cathodes at different potentials, or with one cathode with a large surface in such a manner that the beam more or less fills the cross-section of the interaction space with a ratio E/B that varies proportionally to the distance between the plates of the capacitor. 1

The following figures show non-limitative examples of various tubes that operate according to the principle hereinbefore described.

In Figs. 4 and 4a a tube is shown inside which the radial variation of E/ B, and therefore of the speed of the electrons, is obtained by means of an electrostatic field produced by two cylinders; the electrostatic field therefore varies with r, and the magnetic field at right angles to the plane of the drawing, Fig. 4, may be constant. Fig. 4a shows a cross-section of the tube along E E of Fig. 4. The tube has metal walls, normally of copper, and the cover 41 of this copper box is partly broken away to show the construction of the tube. The electric field of the interaction space is that of a cylindrical capacitor formed by the electrodes 7 and Sin the upper part of the tube. The outer electrode directly forms the wall of the tube which, for use, is generally grounded. A negative voltage with respect to 7 is applied to the inner electrode 8 by means of the lead-in Wire 9. -The electron gun comprises the cathode 10, a focusing electrode 11 and the accelerating anode 12.v The beam produced by this gun is of finite cross-section, in such a manner that while it is passing through the interaction space, the value E/ B varies suificiently in the cross-section of the beam.-

The modulation of the beam is effected by-means of a helix 13 placed between the gun and the entrance of the interaction space. One end of the'helix is connected" to the wall 7, the other to the inner conductor 14 of a coaxial line with the-outer conductor 15 serving for coupling the.

signal generator, an antenna or a pre-amplifying tube for example. The coupling of the load. touthe output is effected in the same manner. The beam passes through "6 thehelix 16, the end of which is connected to the inner conductor 17 of the coaxial line 17, 18. The beams transfer their A. C. power to this output helix and generate a wave, this useful power being transferred to the load coupled to 17, 18.

The input helix 13 and the output helix 16 may be of circular or rectangular cross-sections. The use of helices has, as compared with other forms of circuits hereinafter described, the advantage of providing a very wide bandpass, which is a favorable fact in many cases of use of the tube.

After they have passed through the helix, the beams are collected by the collector 6, the potential of which is equal to that of the outer walls and therefore to that of the positive electrode of the interaction space. The collector can be cooled by compressed air or by water according to the well known methods which are not shown in the figure.

Fig. 4a which shows the section E E of Fig. 4, shows some further details of construction. The inner electrode 8 of the electric capacitor, which is supplied by means of the lead-in wire 9, is supported by the outer walls 41 of the tube and is insulated from said walls by insulating members 19 of ceramic material or quartz for example. In Fig. 4a the electron beam passes through the interaction space 20 in the direction at right angles to the plane. 21 are the pole pieces of the magnet.

Fig. 5 shows a tube which differs from that of Fig. 4 by the shape of the output circuit. Instead of a helix, the tube has an output circuit a cavity 24 which can be tuned to the frequency of the signal by means of adevice that enables a deformation of the walls to be produced, said device not being shown in Fig. 5. At the outlet of the interaction space the beams enter the cavity through a grid 23 comprising fins for example, leave the cavity through a second grid 23 and are collected by the collector 6. A coupling loop 22 is used for collecting the useful power, the load being coupled by means of the coaxial line 17, 18.

Fig. 6 shows a modification provided with a different input circuit. Whereas in the tubes of Figs. 4 and 5 the modulation of the beams was obtained by means of a helix, in the tube of Fig. 6 a grid 25 is placed in front of the cathode. This grid is connected to the inner conductor 14 of the input coaxial line. The input voltage is applied to said grid, which preferably comprises fins, and the density modulation of the beams which is necessary for the operation of the tube is thus obtained. The other features of the tube are the same as those of the tube of Fig. 4, the essential elements being denoted by the same reference numerals as in Fig. 4.

The tube shown in Figs. 7 and 7a uses several modifications as compared with the previously described tubes. The interaction space is also a cylindrical capacitor. However, the distance between the two conductors '7 and 8 is small as compared with the radius of curvature of these electrodes, so that the electrostatic field is almost constant between these two electrodes. Consequently, in order to obtain the desired variation of E/B, it is necessary to produce a non-homogeneous magnetic field in the interaction space.

Furthermore, the input and output circuits in the tube of Fig 7 are retardation guides, the retardation being obtained by means of a large number of perforated discs 26 inserted in a guide of cylindrical cross-section. It is 1 known that an electron beam introduced into such a guide 13 density modulated by a wave which is propagated inthis retardation guide at a speed which is approximately equal to that of the electrons. The signal is applied to the guide by means of a'coaxial line 27, 28, the inner conductor 27 of which contains the cathode 10.- In order to match the generator with the perforated disc guide, the openings of the discs 29 are larger adjacent the inlet than at the outlet of said guide. This variation Of the diameter of the holes causes the charac teristic impedance and the speed of propagation to vary slowly along the path of the incoming signal and the reflection of the signal wave to be reduced to a minimum. At the outlet the beam passes through the output guide in which perforated discs are also inserted. The density-modulated beam transfers its A. C. power to such a guide if the dimensions of the guide and of the perforated discs are so chosen that the speed of the wave generated is the same as that of the electrons. The dimensions of the retardation guide therefore have to be matched with the D. C. operating voltage of the tube. The useful power is transferred to a coaxial line having an outer conductor 30, the inner conductor being the collector 6 for the electrons. As in the input circuit, the matching of the retardation guide with the coaxial line is obtained by means of a variation of the openings of the discs inserted in the guide.

During its travel through the input and output circuits the beam can be focused by means of auxiliary coils 31 and 32.

Fig. 7a shows the section F, F of Fig. 7. In Fig. 7a the electron beams pass through the interaction space 20 between 7 and 8 in a direction at right angles to the plane of the drawing. 21 denotes the pole pieces of the magnet with a gap of variable width for producing the non-homogeneous variable magnetic field between the conductors 7 and 8 of the electrostatic field.

It should be pointed out that the construction of Fig. 7 is only given by way of example and that the principle of this construction allows of numerous modifications. The perforated disc retardation guide can be replaced by a guide in which the retardation is obtained by means of a large number of fins. Furthermore it is possible to replace the coaxial lines 27, 28 at the input and 29, 30 at the output, by other means for coupling the generator or the load respectively. Moreover, this construction is in no way restricted to the shape in which the electron beams describe semi-circles in the interaction space. It is also possible to embody the principle of the construction of Fig. 7 in such a manner as to obtain a fiat tube, similar to the structure shown in Fig. 8. The general principle of the structure of Fig. 7 is as follows: the control of the beam and the collection of the useful power are effected by means of a retardation guide, the retardation being obtained by means of a large number of obstacles in the path of the wave.

The use of such a retardation guide has the advantage that the coupling between the electron beams and the wave generated by the signal is very tight; this means, in practice, that for a given signal power, the density modulation at the entrance of the interaction space is high, higher than that produced by a helix for example. Owing to this intense modulation a high gain of the tube is obtained. On the other hand, the band-pass of a tube provided with circuits in the form of a guide containing obstacles is narrower than that of a helix.

Although Fig. 7 shows the embodiment of the principle of a non-homogeneous magnetic field in the case of a tube with a constant electrostatic field in the interaction space, it is of course to be understood that it is also possible to have a combination of a certain degree of non- V homogeneity of the electrostatic field with a certain degree of non-homogeneity of the magnetic field.

Figs. 8 and 8a show a tube of fiat structure with two cathodes a and 10b which can be raised to diiferent negative voltages with respect to the common anode 12. The transverse electric field is applied between the fiat electrode 8 provided with a lead-in wire 9 and the metal wall 7 of the tube, 7 being positive with respect to 8. Since the electrostatic field is constant between 7 and 8, it is necessary to have a non-homogeneous magnetic field produced by a magnet provided with pole pieces 21. with a gap of variable Width. With suitably chosen values of E, B and of the biases of the cathodes 10a, 10b and of the focusing electrodes, it is possible to cause the beams,

when there is no signal, ot pass through the interaction space along straight lines. At the input end, the control is elfected by means of a helix 13, the signal generator being coupled to said helix by the coaxial lines 14, 15. The load is coupled to the output helix 16 by the coaxial lines 17, 18. The axis of this helix should preferably be slightly inclined relatively to the-axis of the tube so as to take into account the shape of the electron trajectories which is produced by the presence of the signal. 6 is the collector which maybe cooled with compressed air or with water.

It should be pointed out, as an important fact, that the diflerent biasing of the two cathodes is not sufficient for obtaining difierent speeds in the intersecting electric and magnetic fields. The average speed of the electrons depends only on the ratio E/B and is independent of the bias of the cathode. The only purpose of the different biases of the cathodes is to obtain sufliciently straight trajectories for the electrons between the input and the output. Without a suitably chosen bias, the beam would impinge on one of the electrodes 7 or 8 before it had passed the output helix. On the other hand, the average speed of the electrons and the variation of said speed in the interaction space are determined only by the values of the electric field and the magnetic field.

In Figs. 4 to 7 the tubes contain only one cathode. It is of course to be understood that in these structures it may also be advantageous to use two or even a larger number of cathodes. Conversely, the flat system of Fig. 8 is not restricted to the use of a plurality of cathodes and will also operate with a single cathode, the use of a plurality of cathodes being, however, advantageous as regards the gain and the efficiency of the tube.

Figs. 9 and 9a show a fiat tube which differs from that of Fig. 8 by the method for enabling the variation of the speeds of the electrons to be produced in the interaction space. A homogeneous magnetic field is applied to this tube, i. e. the width of the gap between the pole pieces 21 of the magnet is constant over the entire height of the interaction space. The electric field is applied between 8 and 7, 8 being negative with respect to 7. In order to obtain a variation of the electric field in each cross-section, a number of cathodes 33 are inserted in the interaction space and the current of said cathodes is emitted in said space. The space charge which is produced thereby causes a decrease of the potential in the interaction space; the electric field decreases near 8 and is increased near 7. A variation of the current emitted by the cathodes 33, obtained by heating them more or less through the lead-in wires 34, enables the value of the potential between 8 and 7 to be varied and the best conditions of operation to be obtained.

Tests have shown that the structure of Fig. 9 is also capable of operating without the cathodes 33 if the current density of the beams is sufliciently high. In this case, the space charge of the actual beams is already sufiicient to produce a variation of the transverse electric field and thus obtain a variation of the speed of the electrons which is necessary for the operation of the tube.

What we claim is:

l. A travelling wave tube comprising a pair of electrodes having smooth surfaces defining therebetween an interaction space with entrance and outlet portions, means comprising connections to said electrodes for applying a potential difference therebetween for establishing an electric field having its lines of force directed transversely across said space, a source of electrons located near the entrance of said space and provided with means for introducing into said space a plurality of electron streams directed perpendicular to the lines of force of said electric field, means located outside the tube for applying to the interaction space a magnetic field having its lines of force directed at right angles to the lines of force of said electric field and to the direction of said electron streams, the velocity of each stream at each point thereof being substantially equal to the-ratio of intensities of said electric and magnetic fields at said point, said intensities being stated in homogeneous units, physicalmeans imparting different velocities to various streams by disturbing uniformity of said ratio along transverse sections of said space, means acting on at least one electron stream at the entrance of the interaction space for density modulating said one stream by ultra-high frequency energy, and means coupled to the outlet of the interaction space for collecting the ultra-high frequency energy contained in the streams.

2. Tube according to claim 1, wherein the means for imparting respectively different velocities to the various electron streams comprise means for giving to the ratio of intensities of said electric and magnetic fields values that vary in space transversely with respect to the electron streams and wherein means are provided for rendering the intensity of electric field variable in space transversely with respect to the electron streams, said last mentioned means comprising at least one emitting cathode located adjacent a portion of the interaction space intermediate said entrance and outlet portions so as to alter the space charge by means of its emission.

3. Tube according to claim 1, wherein the means for collecting the energy contained in the streams comprise a helix coupled to the electron streams at said outlet portion of the interaction space, and output terminal means coupled to said helix, the axis of said helix being inclined with respect to the mean axis of the electron trajectory.

4. Tube according to claim 1, wherein the physical means for imparting respectively different velocities to the various electron streams comprise a circularly bent shape of said electrodes for rendering the intensity of the electric field variable in space transversely with respect to the electron streams, whereby the ratio of the intensities of said electric and magnetic fields varies in space transversely with respect to said electron streams.

5. Tube according to claim 4, wherein the electrodes that bound the interaction space are curved to form a cylindrical capacitor.

6. Tube according to claim 1, wherein the physical means for imparting respectively different velocities to the various electron streams comprise means for giving to the ratio between the intensities of said electric and magnetic fields values that vary in space transversely with respect to said electron streams, said last named means comprising a magnet for producing said magnetic field, said magnet having pole pieces and a gap between said pole pieces which varies in the transverse direction with respect to said electron streams for rendering the intensity of said magnetic field variable in space transversely with respect to said electron streams.

7. Tube according to claim 1, wherein the source of electrons comprises a single cathode for emitting a beam containing a plurality of electron streams travelling at different velocities.

8. Tube according to claim 1, wherein the means for density modulating the electron streams comprise a grid positioned in the path of the electrons, and terminal means for applying a modulating signal to said grid.

9. Tube according to claim 1, wherein the means for density modulating the electron streams comprise a waveguide section having the properties of a delay line for ultra-high frequency energy, means coupling said waveguide section to the electron streams before entering said interaction space, and means for introducing an electro magnetic wave into said wave-guide section.

10. Tube according to claim 9, wherein impedance matching means are provided at the entrance of said wave-guide section.

11. Tube according to claim 1, wherein the means for collecting the energy contained in the streams comprise a '10 cavity coupled to the'electron streams at said outlet portion of the interaction space.

l2. Tube according to claim 11 further comprising means for tuning said cavity to the frequency ofsaid enrgy. r

13. Tube according to claim 1, wherein the means for collecting the energy contained in the streams comprise alwave guide section having t e. Properties of a delay line for ultra-high frequency energy, 'means coupling said wave-guide section to the electron streams at said outlet portion of the interaction space.

14. Tube according to claim 13, wherein impedance matching means are provided at the outlet of said wave guide section.

15. Tube according to claim 1, said tube further comprising an electron collector and wherein the means for collecting the energy contained in the streams comprise an oscillating circuit connected to the electron collector.

16. A travelling wave tube comprising a pair of electrodes having smooth surfaces defining an interaction space therebetween with entrance and outlet portions, means comprising connections to said electrodes for establishing an electric field having its lines of force directed transversely across said space, a source of electrons located near the entrance of said space and provided with means for introducing into said space a plurality of electron streams directed perpendicular to the lines of force of said electric field, means located outside the tube for applying a magnetic field to the space, the velocity of each stream at each point thereof being substantially equal to the ratio of the intensities of said electrio and magnetic fields at said point, said intensities being stated in homogeneous units, physical means imparting different velocities to various streams by disturbing uniformity of said ratio along transverse sections of said space, comprising at least one emitting cathode located in the interaction space so as to alter the space charge, electrical means acting on at least one electron stream at the entrance of the interaction space for density modulating said one stream by ultra-high frequency energy, and means coupled to the outlet of the interaction space for collecting the ultra-high frequency energy contained in the streams.

17. A travelling Wave tube comprising a tube of electrodes having smooth surfaces defining an interaction space therebetween with entrance and outlet portions, means comprising connections to said electrodes for applying a potential difference therebetween for establishing an electric field having its lines of force directed transversely across said space, a source of electrons located near the entrance of said space and provided with means for introducing into said space a plurality of electron streams directed perpendicular to the lines of force of said electric field, means located outside the tube for applying a magnetic field to the space, the velocity of each stream at each point thereof being substantially equal to the ratio of the intensities of said electric and magnetic fields at said point, said intensities being stated in homogeneous units, physical means imparting different velocities to various streams by disturbing uniformity of said ratio along transverse sections of said space, electrical means acting on at least one electron stream at the entrance of the interaction space for density modulating said one stream by ultra-high frequency energy, a helix coupled to the electron streams at the outlet portion of the interaction space having its axis inclined to the mean axis of the electron trajectory for collecting the ultra-high frequency energy contained in the streams and output terminal means coupled to said helix for transfer of energy to an outside circuit.

11 UNITED STATES PATENTS Kleen et al. June 13, 1950 Doehler et a1. Nov. 28, 1950 Tiley Feb. 13, 1951 Lerbs Aug. 28, 1951 Pierce Feb. 12, 1952 Clavier et a1. Sept. 8, 1953 Hollenberg Sept. 15, 19.53

12 OTHER REFERENCES Article entitled Analysis of a Simple Model of a. Two- Beam Growing-Wave Tube, pp. 585-601, RCA Review, December 1948.

Article entitled The Electron-Wave Tube, pp. 410, Pros. I. R. E., January 1949.

Article :by Hollenberg, pp. 52-58, Bell System Tech. Ioun, January 1949.

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